A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used to identify materials. The variable measured can be the light's spectral intensity or irradiance. Fourier transform spectrometers can be used for visible, infrared and ultraviolet frequencies, and are based on two-beam interference or polarization modulation phenomenon to generate a resulting interferogram. The Fourier transform of a resulting interferogram corresponds to the spectral signature of incoming light.
One type of Fourier Transform interferometer uses birefringent optics to create polarization modulation with the angle of incidence of light and generate fringes across the field of view of an optical imager. For example, WO 2011/093794 to Phua et al discloses an advanced hyperspectral imaging device which provides spectral signatures of every point of a 2D image. A cascade of birefringent plates is used to generate linear (or curved) fringes which are relatively easy to process. While Phua et al is an elegant device which greatly simplifies optics required for generation of interferograms, the device requires scanning, that is, a large plurality of images have to be taken. Extensive computational processing is also needed to process the large plurality of images to give the spectral signatures of every point of the image. The large processing requirements for such a hyperspectral imaging device will not work well with digital cameras, especially those found in mobile devices. This is due in part to the relatively limited processing power available in mobile devices. Further, jitter during scanning will lead to the introduction of high spectral inaccuracies.
Other known spectrometers are relatively difficult to use with field work outside of a lab, and they are typically much more expensive, require frequent spectral recalibration, require several display/control/power accessories before the spectrometer can function properly, and are simply too bulky and inconvenient to carry around while running a daily routine. As such, spectrometers, although highly useful analytical instruments, have seen limited adoption by the general public and are normally restricted to lab work. It would be desirable to provide a spectrometer which is small enough to be used with existing digital cameras, especially those incorporated into conventional mobile devices, and which is lightweight and convenient enough to carry around while running a daily routine. It is also would be desirable to provide a spectrometer which does not require mechanical scanning, and which can capture a spectral signature of an object in a single snapshot while only requiring the simple processing power that mobile devices can handle while still maintaining a high level of spectral fidelity to allow for accurate and rapid analysis.